class Person{
    username:string;
    age:number=10;
    constructor(username:string){
        this.username = username;
    }

    sayAge():void{
        console.log(this.age)
    }
}

let person = new Person('zs');

class Student extends Person{
    constructor(username:string){
        super(username);
    }

    test():void{
        console.log(this.age)
    }
}

person.sayAge();

let s1 = new Student('asas')

s1.test()

console.log(person.age)

